Field of the Invention
The present invention relates to an on-board assembly for producing and storing electricity, which can be used in particular on a sailing boat in order, for example, to supply the on-board electronic equipment.
Brief Discussion of the Related Art
Such an assembly generally comprises a hydrogenerator having an output line connected to electrical accumulators having predetermined electrical charging parameters. The hydrogenerator comprises a carrying structure on which a generator with permanent magnets and an impeller secured to a driveshaft of a rotor of the generator are mounted, so that the carrying structure can be fastened to the stern of a sailing boat while keeping the impeller submerged. The output of the generator is connected to a rectifier circuit connected to a DC/DC converter connected to the accumulators, in such a way that the hydrogenerator supplies the accumulators with a substantially constant DC voltage.
It will be understood that, when the sailing boat is in motion, the impeller turns under the effect of its movement in the water and drives in rotation the rotor of the generator, which then produces a current for charging the accumulators.
As the rotational speed of the impeller increases, the generator supplies more and more electrical power but, at the same time, generates a larger and larger resisting torque on the driveshaft of the motor. Thus, the resisting torque generated on the shaft of the impeller by the generator brakes the rotation of the impeller and prevents the impeller from reaching the rotational speed which it would have if it pivoted freely in the wake of the sailing boat. This results in drag which is detrimental to the performance of the sailing boat, in particular for competition sailing boats, and more particularly for racing at sea, for which the maximum speed is an essential characteristic.
In order to avoid this drawback, it is known to use a variable-pitch impeller. In this type of impeller, the blades are mounted on pivoting radial axles making it possible to modify the pitch of the impeller. Thus, with this type of impeller, the pitch of the impeller is increased in order to reduce the drag which it causes as the speed of the boat increases. Although this solution is attractive in terms of its principal, it is nevertheless complex to implement. The orientation control of the blades of the impeller employs an electromechanical actuator or an actuator with hydraulic means driven by a computer, so that this solution finally proves to be heavy and complex. Furthermore, despite this complexity, the desired result is only partially achieved because the means employed entail a long pitch correction time. This results in a significant variation of the output voltage of the generator, which makes the aforementioned DC/DC converter indispensable and means that the output voltage may reach high values. It is known to provide an electronic peak clipper in order to partially mitigate the latter drawback. Such a peak clipper makes the system even more complex, however, and when it is acting it consumes a high current at the clipping voltage as pure loss. This results in an energy loss and a superfluous increase in the resisting torque applied to the impeller, and therefore the drag (resistance to moving forward) which it produces. Furthermore, because of the very principle of an unregulated generator, the voltage of which cannot be reduced too much without having too high a current, and therefore heavy transport cables with a large cross section, and the easiest DC/DC converter to produce, which is a step-down converter, its output voltage is particularly high and considered dangerous for a user in a wet environment.